Summary: Intact cells of (NCTC 1937) after growth under O-limited conditions in batch culture exhibit, in addition to - and -type cytochromes, an unusual pigment absorbing variably at 588 to 594 nm in reduced oxidized difference spectra at room temperature. CO difference spectra suggest ligand binding by this pigment and also reveal a prominent 448 nm absorption minimum and CO-binding - and/or -type cytochromes. Although the 588 to 594 nm-absorbing component is reminiscent of “cytochrome ”, claimed to be a terminal oxidase in some bacteria, O-limited cells of contain no detectable haem A. In contrast, cells grown under O-sufficient conditions exhibit a membrane-bound cytochrome and contain haem A. Low-temperature photodissociation studies of O-sufficient cells show cytochrome to be functional in CO and O binding and suggest that is the terminal oxidase of a cytochrome - and -containing aerobic respiratory chain. Analogous studies of O-limited cells reveal a component absorbing, in its unliganded state, at 448 nm. Exposure of such CO-liganded cells to white actinic light is followed by oxidation of - and/or -type cytochromes and, although the functional oxidase has not been identified, we conclude that does not utilize a cytochrome oxidase of the type.


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